Classification

Higher order taxa

Species

Description and significance

Cross Section of L. Patella. The green portion are the P. didemni cells

P.didemni Cells.

Prochloron Didemni is a unicellular cyanobacteria that is photosynthetic and oxygenic. It is an obligate symbiont that lives in the ascidian Lissoclinum patella and can be found in marine environments.

The study of Prochloron didemni and its genome can provide us with valuable information. The genome of P. didemni is currently incomplete. However, when completed, P. didemni's genome can be used for analysis to elucidate other genes responsible for symbiosis between bacteria and chordates, such as humans. Also, as a oxygenic, photosynthetic cyanobacteria, P. didemni is a significant player in global carbon fixation. The study of its metabolic pathways and unique photosynthetic processes would yield information beneficial to biotechnology.

R.A. Lewin first discovered Prochloron didemni in 1975, but identified it as Synechocystis didemni. In 1977, the presence of chlorophyll a/b and the lack of phycobilins caused it to be transfered to a new genus, Prochloron, and named Prochloron didemni.(4)

Genome structure

The complete genome for Prochloron didemni has not been sequenced but is estimated to be aproximately 5 million base pairs long with a molecular weight of 3.59x10^9 daltons.(8,10) This estimate was reached by assembly of 82,337 shotgun reads and Glimmer, a gene-finding software.(10) Denaturation kinetics revealed a Tm of 70.6°C, indicating a GC composition of 40.8 mol%.(8)

P. didemni possesses homologs to genes gap2 and gap3, glyceraldehyde-3-phosphate dehydrogenase genes, from Anabaena. These genes are needed to produce GADPH, which is used in the Calvin cycle to metabolize carbon.(6) Genes patA-patG have also been identified, which code for the machinery necessary for patellamide biosynthesis.(1)

Cell structure and metabolism

Prochloron didemni are photosynthetic cyanobacteria with a twist. They carry out photosynthesis similar to Eukaryotic plants, with two reaction centers in noncyclic electron flow.(7) However, unlike cyanobacteria, P. didemni have chlorophyll a and b and lack phycobiliprotiens.(2) Photosynthesis takes place in the thylakoids, with the thylakoids concentrated toward the periphery of the cell.(7)

The cell wall of Prochloron didemni consists of peptidoglycan and muramic acid of the A1 γ type. Approximately 40% cross-linkage exists in P. didemni's cell wall with a network of five to eight layers and a thickness of 12nm.(9)

Describe any interesting features and/or cell structures; how it gains energy; what important molecules it produces.

Ecology

Lissoclinum patella Colony

Prochloron didemni is an obligate symbiont that lives in the ascidian Lissoclinum patella. L. patella along with P. didemni can be found in tropical waters, such as the reefs in Hawaii and the Great Barrier Reef in Australia.(2,7)

Exchange of nutrients is the main reason for the symbiotic relationship between L. patella and P. didemni. Photosynthesis by P. didemni provides 60-100% of the organic carbon needed by L. patella. There is also evidence that suggests there is nitrogen cycling between the host and symbiont as well as nitrogen fixation. In exchange for the organic carbons and nitrogen cycling, L. patella provides optimal growth conditions by moving to areas with proper sunlight and a tunic covering.(1)

Patellamides, a product of P.didemni, also play in role in the symbiosis. The cytotoxic characteristic of patellamides may be used as feeding deterrents and patellamides' ability to chelate metals, such as copper and zinc, may be used in detoxification.(1)

Application to Biotechnology

Patellamide C

One of the major problems with treating cancer is multi drug resistance. A recent study on Prochloron didemni revealed that it produces Patellamides A and C, which can be used to reverse multi drug resistance in cancer cells.(1)

Patellamides are psuedosymmetrical, cyclic dimers. Each substructure of patellamide contains the specific sequence thiazole-nonpolar amino acid-oxazoline-nonpolar amino acid. Study show that patellamides A and C are ribosomally synthesized and encoded on a single ORF. Genes patA - patG are responsible for the biosynthesis of patellamides. It is currently known that patA codes for a Subtilisin-like protease, patD for an adenylating enzyme-hydrolase hybrid, patE the precursor peptide, and patG a oxidoreductase-protease hybrid. Functions of patB,C,& F are still unknown.(1)

Current Research

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